This invention relates to a thin, calendered airlaid composite which may or may not include additional sheet layers to form a multi-layered absorbent structure. The airlaid composite is useful as an absorbent article, (e.g. absorbent pad), particularly in the meat and poultry industry for absorbing exudate in packaging. This invention also includes a process for making such an airlaid composite.
This invention relates to airlaid composites and absorbent structures for use as absorbent articles which may be particularly useful in the meat and poultry packaging industry for absorbing exudate. To absorb this exudate, the absorbent pads are generally placed within the package along with the meat or poultry.
Most absorbent pads of the prior art which are used for absorbing exudate from food products consist of absorbent layers which are generally multi-ply layers of tissue, paper toweling and/or wood fluff. The prior art pads tend to have limited absorbency and tend to break up when saturated with exudate. To overcome the tendency to break-up, the prior art pads may be encased (sealed around the peripheral edges) between fluid impervious and fluid pervious layers, which is both costly and difficult to process.
The present invention is distinguished from prior art absorbent pads in that the prior art pads are generally loose, high loft, bulky materials. As a matter of fact, this lofty aspect of many prior art pads is required to achieve absorbency. In the case of absorbent pads formed with tissue or wood fluff, it has been common belief that liquids are absorbed and retained mainly within the empty spaces which are formed in the network of cellulose fibers, rather than absorbed into individual fibers. In such cases, the quantity of liquid absorbed by an absorbent body of cellulose fibers is therefore greater the lower its density, that is, the greater its bulk. Consequently, it has been previously thought that anything which affects the density and can cause the absorbent material to collapse will contribute to a reduction of its absorption capacity. Some pads even include rigid particles to prevent collapse (e.g., nodules, pyramids).
Some prior art pads have attempted to combine binder fibers along with absorbent fibers (e.g. pulp). It should be noted that prior art pads employing binder fibers therein generally have employed such fibers for the purpose of maintaining or establishing high loft in the pad, while providing mechanical integrity to the batt. Additionally, the prior art pads have generally utilized very short binder fibers (having an average length of approximately 1 mm) with the intent that the fibers completely melt and therefore act as a glue which binds the absorbent fibers together. Such pads may have good strength and a capacity for absorbing liquids, but generally will have a fairly low total capacity.
Even with the various embodiments of the prior art pads, most will lose their resilience and the pad will collapse when wetted and subjected to pressure, regardless of the fact that the pulp fibers are interconnected to form a framework. Products such as tissue tend to break apart when wetted. Such materials also readily release their absorbed fluids when placed under a compressive load such as the load of the meat product on the pad and loads such as when packages are stacked one upon the other as in shipping cartons and store displays.
Yet another problem of prior art pads is variability in thickness by as much as xc2x115%. Such thickness variation translates into absorbency variation as well. Variable thickness also affects convertibility issues. Since these materials are usually fed through machines with nip rollers or belts, wide variation in thickness results in slippage and jams in the machines which decreases production rates resulting in higher costs.
In the development of such products, an absorbent structure which provides ample absorbency, has uniform thickness and which will not break up during handling or use, is needed.
As for the process of making such absorbent structures, particularly those including binder fibers, typical airlaid materials with binder fibers are mechanically compacted several times during processing to provide strength such that the airlaid material may be handled during processing. Usually, the airlaid material is compressed by a compaction roll immediately after leaving the airformer. The airlaid composite of the present invention is not compacted in any way prior to heating since the airlaid composite must remain in a lofty array so that proper and thorough bonding may occur. Additionally, unlike conventional airlaid processes, the airlaid composite of the present invention is cooled prior to calendering and the calenders are not heated. By cooling the airlaid composite in this way, the structure is not locked down in a compacted state until after the bicomponent fibers have cooled and re-solidified. The thin, calendered airlaid composites of the present invention thus exhibit unexpectedly good absorbency in both capacity to absorb and ability to retain liquid while being presented in a form which is easy to handle and has strength sufficient to avoid the tendency to fall apart.
The present invention pertains to an airlaid composite which is made of pulp fibers, at least about 2% by weight bicomponent fiber, and moisture. This airlaid composite is unique in that a uniformly even composite is made which upon calendering, becomes a thin structure which maintains significant absorbency when saturated. The bicomponent fibers of the present invention include a first polymer component and a second polymer component, and the first polymer component melts at a temperature lower than the melting temperature of the second polymer component. Mixing of the pulp fibers with the bicomponent fibers is done in such a way that the fibers are evenly dispersed in the airlaid composite. This airlaid composite is then heated such that at least a portion of the first polymer component of the bicomponent fiber is melted, which bond the bicomponent fibers to many of the pulp and bicomponent fibers when cooled. Moisture is added on to the composite to further facilitate bonding when the composite is subsequently subjected to calendering. Optionally, a sheet layer may be attached to the airlaid composite to form a multi-layered absorbent structure. Such composites and absorbent structures are characterized by a drape stiffness of at least about 5 cm, an absorbency of at least about 12 g/g, and a dry tensile strength of at least about 1300 g.